1. Field of the Invention
The present invention relates to a system for generating high resolution computer video display or peripheral device driver signals using computer system video output channels designed for producing lower resolution video signals.
2. Background Information
Computers providing a visual image output using cathode ray tubes (CRT's) normally maintain a data representation of the image in the computer's random access memory (RAM), and periodically transmit these data to the CRT in order to produce the display image. This type of system requires constant refreshing, or rewriting, in order to maintain visible display. Refreshing the display may be accomplished using either dedicated hardware or a combination of hardware and software. The central processing unit (CPU) needs to read and write to the display RAM, therefore there is a contention between the CPU and the circuitry controlling the display. As the resolution, or number of pixels comprising the displayed image increases, additional memory is required for the image, and more and more memory bandwidth must be consumed to maintain the display. There is a limit to the amount of image resolution where eventually the entire memory bandwidth is being used to refresh the display, and no memory bandwidth is available to modify the display. This is a traditional bottleneck in low cost computer architectures.
One attempt to avoid this limitation has been to locate display RAM in a dedicated frame buffer used for display refresh purposes, and to allow the CPU only limited access to that buffer. This often takes place via a dedicated serial, parallel, or direct memory access (DMA) channel. More expensive systems provide a frame buffer with a dedicated CPU responsible for performing operations only on display RAM. Typically in such systems, the dedicated CPU receives commands from the host CPU regarding tasks to be performed.
A second method for increasing resolution without increasing the memory bandwidth requirements for refreshing a display has been to incorporate interlaced displays. This can be done with conventional video monitors or National Television System Committee (NTSC) signals for viewing with conventional home televisions. This typically involves using two frames of video information to refresh the display. One of the frames is the normal display field and the second frame is similar to the first, but offset vertically by one-half a horizontal line. In this way the screen is scanned at 60 Hz. in the normal fashion, but total screen updating occurs at 30 Hz. This often results in objectionable flicker and is annoying to the user. One solution to the flicker problem has been to employ frame buffer techniques to build a scan converter which stores the even and odd visual frames in RAM, and uses that memory to drive a display at a higher bandwidth, achieving a (nominally) 60 Hz. refresh of the entire display. In this type of design, the interlaced output PG,4 from the host is different for even and odd frames, and therefore can be considered to have encoded information indicating which type of display field is being updated, either even or odd. Scan converters arguably increase the vertical resolution of the display, but do not increase the horizontal, temporal, or color resolution.
Frame buffer and scan converter techniques restrict the use of a computer video output terminal to a single device and they also rarely exploit regions of the computer output video signals that contain no useful data, such as during the horizontal and vertical blanking intervals. It is possible to encode data in these regions for other purposes and also to encode data in the video output signal by modifying sync signals.
It is an object of the present invention to provide a system and method for generating high horizontal and vertical resolution video frame data using conventional computer device video output channels designed for driving lower resolution, non-frame buffered displays.
It is another object of the present invention to provide a system and method for decoding information encoded in a single host computer video output signal and distinguishing that information from conventional video data normally output by such a computer, allowing control of a plurality of devices using such encoded data.
Yet another object is to provide a system and method and for using a conventional frame buffer to derive a display of arbitrary spatial, color, or temporal resolution. Data in this frame buffer are updated by addressing individual regions of the frame buffer via the control information encoded in the computer output video signal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.